As the technique for the modification of the surface condition of a polymer molded article, particularly a polymer film, there have been proposed many methods employing chemical or physical means. In particular, the use of a film as a recording material is rapidly growing recently, and the surface modification of such a film is a requisite and essential technique.
Meanwhile, the use of a high output ultraviolet laser such as excimer laser has recently been proposed as a means for the modification of a polymer molded article. Description is made below on typical literatures describing the use of such an ultraviolet laser.
(1) "Laser Research", Vol. 8, No. 6, 941 (1980):
This treatise entitled "Photoetching of PMMA by Excimer Laser" by Yoshiyuki Kawamura et al. describes the effect of the application of a KrF laser beam to a polymethyl methacrylate (PMMA) under different power densities and different fluences (energy densities), on the etching depth of the PMMA.
(2) Specification of U.S. Pat No. 4,247,496:
This patent describes a method for modifying the surface of a polypropylene film or a polyethylene terephthalate film by drawing the film after or simultaneously with the application of an ultraviolet light using an ultraviolet lamp. The patent describes that by a combination of the ultraviolet light application and the drawing, the film is improved in slipperiness, loses gloss, is improved in hygroscopicity and oil absorbability, and acquires drawability.
Therefore, the patent discloses a method for modifying the surface of a polypropylene film, a polyethylene terephthalate film or the like by a combination of drawing and ultraviolet light application under the above mentioned condition but makes no disclosure as to the method for modifying the surface of a film by ultraviolet light application alone.
(3) Appl. Phys. Lett. 43 (8) 717 (1983):
This treatise entitled "Direct etching of polymeric materials using a XeCl laser" by J. E. Andrew et al. describes that when a polyethylene terephthalate film is irradiated with a XeCl laser beam, the irradiated portion of the film is decomposed and etched. The treatise also describes that a polyimide and a photoresist are etched as well.
(4) IBMT Technical Disclosure Bulletin Vol. 26 No. 63049 (1983):
This treatise entitled "Archival Storage with UV Lasers" by S. E. Blum et al. describes that when a polymer is irradiated with a laser having a wavelength of 200 nm or less, the irradiated portions of the polymer momentarily cause ablation effectively and that the utilization of this ablative feature enables high density information recording in polymer material at a low fluence (energy density).
In this method, however, when a polymer material is irradiated with a laser at a fluence close to the threshold in order to cause ablation and enable information recording therein, the difference in reflectance between the irradiated and non-irradiated portions of the polymer material is not striking in spite of the occurrence of ablation. The enlargement of difference in reflectance requires the use of a laser beam having a higher energy density and a short wavelength of 200 nm or less. Thus, the above method has drawbacks.
(5) Laser Processing and Diagnostics, Proceedings of an International Conference, University of Linz, Austria, Jul. 15-19, 1984, pp. 343-353:
In this treatise entitled "Ultraviolet Laser Ablation of Organic Polymer Films", R. Srinivasan describes that when films of polymers such as polyethylene terephthalate, polyimide, polymethyl methacrylate and the like were irradiated with several ultraviolet laser beams of different wavelengths, etching was seen on the film surfaces.
The treatise describes that the ablation has a threshold and takes place only when the laser application is made at a fluence of certain given value or more. This "threshold" differs by the type of polymer irradiated and also by the type of laser used for irradiation. According to R. Srinivan et al., the threshold for, for example, polycarbonate is as follows.
______________________________________ Type of U.V. laser (wavelength) Threshold ______________________________________ XeCl (308 nm) About 300 mJ/cm.sup.2 KrF (248 nm) About 200 mJ/cm.sup.2 ArF (193 nm) About 50 mJ/cm.sup.2 ______________________________________
From the above relation between wavelength and threshold in polycarbonate, it is appreciated that when a laser beam of long wavelength is applied in order to cause ablation, a high fluence is required.
(6) J. Phys. Chem. 1986, 90, 2124-2134:
This treatise by S. Lazare et al. describes that when a polyethylene terephthalate film is irradiated with an ArF excimer laser beam at a fluence of 100 mJ/cm.sup.2 per pulse in air and the film surface is observed with a scanning type electron microscope, fine unevennesses are seen on the surface.
(7) Appl. Phys. 64 (1) 365 (1988)
This treatise entitled "Structural origin of surface morphological modification developed on poly (ethylene terephthalate) by excimer laser photoablation" by Y. Novis et al. describes the results of application of an ArF laser beam to undrawn and uniaxially drawn polyethylene terephthalate films.
According to the treatise, the surface of the undrawn film is etched uniformly with the transparency remaining, while on the surface of the uniaxially drawn film, there are formed unevennesses aligned in a direction perpendicular to the drawing direction. It is further described that the condition of surface etching is strikingly different between the amorphous film and the semicrystalline film and accordingly the surface etching by an ultraviolet laser beam provides a rapid and simple method for observation of the structure of a semicrystalline aromatic polymer.
(8) Specifications of U.S. Pat. Nos. 4,414,059, 4,417,948 and 4,568,632:
These U.S. patents propose a method for etching a film of a polymethyl methacrylate, a polyethylene terephthalate or a polyimide using an ultraviolet light having a wavelength of 220 nm or less.
In the above mentioned conventional techniques by irradiation of a polymer with an ultraviolet laser beam, the core of technique lies in the etching of a polymer molded article, and the polymer to be treated is an aliphatic polymer or a very restricted particular monocyclic aromatic polymer.
Hence, the present inventors made intensive research on the use of an ultraviolet laser beam to modify the surface of a polymer molded article and found interesting facts as shown below.
(a) It was found that even when an aromatic polymer molded article is irradiated with a laser beam having a longer wavelength than employed in the conventionally known techniques or at a lower fluence, the modification of the surface of the molded article, particularly its discoloration such as whitening or blackening takes place efficiently when the pulse frequency is increased. Under such condition of irradiation with an ultraviolet leaser beam, the surface of the polymer molded article causes discoloration at a fluence lower than the threshold.
That is, it was found that when the fluence is considerably lower than the threshold, the surface of the polymer molded articles is transparent but the irradiated site can be clearly observed with the naked eye and, when the fluence is increased, the surface whitens, and at a fluence slightly higher than that, the surface blackens, and the surface becomes white again when the fluence is made still higher.
It was found that the difference in color (e.g. surface reflectance) between the irradiated and discolored portions and the non-irradiated portions is very large. It was found moreover that the discoloration is difficult to peel off from the surface of the molded article and the change in surface reflectance differs only very slightly between different lights of different wavelengths used for reading-out and thus the irradiated molded article has characteristics which are very advantageous practically.
(b) When an ultraviolet laser beam is used in place of a discharge lamp such as mercury lamp, the surface of a molded article irradiated therewith is modified even without effecting drawing simultaneously with or after the irradiation. That is, a phenomenon was seen which was different from the description in the specification of U.S. Pat. No. 4,247,496 that the surface of a uniaxially or biaxially drawn molded article is modified when the surface is irradiated with an ultraviolet laser beam. The degree of the surface modification or discoloration can be adjusted or controlled by changing the irradiation conditions by an ultraviolet laser beam. In this case, more striking modification is seen by the use of a drawn molded article.
(c) It was found that a polymer having, in the recurring unit constituting the polymer, at least one polycyclic condensed aromatic ring or diphenyl ring such as naphthalene ring or anthracene ring can easily cause surface modification, i.e. etching even by using a discharge lamp of wavelength shorter than 380 nm (e.g. high pressure mercury lamp, xenon lamp, carbon arc), in place of using an ultraviolet laser of wavelength of 200 or less or a high output ultraviolet laser. That is, it was found that when an ultraviolet laser beam is used for irradiation of a polymer molded article, the molded article can be subjected to photoprocessing in a state that substantially no thermal history remains, even by using an ultraviolet laser beam of longer wavelength than employed in the conventional techniques.
The present invention has been reached based on the above findings and includes the following inventions.
1. A process for producing a molded article having a modified surface condition as a result of the irradiation with an ultraviolet laser beam, which process is characterized by irradiating the surface of a molded article composed of an aromatic polymer or a polymer composition containing said aromatic polymer
(a) with an ultraviolet laser beam having a wavelength of about 150 nm-380 nm, PA1 (b) at a density of at least 10.sup.4 w/cm.sup.2, and PA1 (c) at a fluence lower than the threshold. PA1 (a) with an ultraviolet laser beam having a wavelength or about 150 nm-380 nm, PA1 (b) at a density of at least 10.sup.4 w/cm.sup.2, PA1 (c') at a fluence which is 300% or less of the threshold, PA1 (d) so that the surface portions irradiated with the ultraviolet laser beam are discolored. PA1 (a') with an ultraviolet laser beam having a wavelength of 220 nm-380 nm, PA1 (b) at a density of at least 10.sup.4 w/cm.sup.2, and PA1 (c) at a fluence lower than the threshold.
2. A process for producing a molded article having an at least partially discolored surface as a result of the irradiation with an ultraviolet laser beam, which process is characterized by irradiating the surface of a molded article composed of an aromatic polymer or a polymer composition containing said aromatic polymer
3. A process for producing a molded article with a modified or etched surface, which process is characterized by irradiating the surface of a molded article composed of a linear polymer composition constituted by a recurring unit containing at least one polycyclic condensed aromatic ring or diphenyl ring, with an ultraviolet light having a wavelength of about 150 nm-about 380 nm.
4. A process for producing a polyethylene terephthalate molded article having a modified or discolored surface condition as a result of the irradiation with an ultraviolet laser beam, which process is characterized by irradiating the surface of a molded article of an at least uniaxially drawn polyethylene terephthalate
The present invention is described in more detail below.
In the present invention, the molded article to be irradiated with an ultraviolet laser beam is composed of an aromatic polymer or a composition containing said aromatic polymer, preferably of a composition containing an aromatic polymer in an amount of about 20% by weight or more, desirably about 50% by weight or more, particularly about 70% by weight or more.
The aromatic polymer refers to an aromatic polymer containing at least one aromatic ring in the monomer unit constituting the polymer when the monomer unit is one kind, or containing at least one aromatic ring in at least one monomer unit when the monomer units are two or more kinds. The aromatic ring is preferably an aromatic hydrocarbon ring of 6-14 carbon atoms such as benzene ring, naphthalene ring, anthracene ring or diphenyl ring.
As the bonding form of the aromatic polymer, there can be mentioned ester, amide, imide, ether, ketone, sulfone, sulfide, carbonate, epoxy or alkylene.
The molded article of the present invention preferably contains about 20% by weight or more of the aromatic polymer. The molded article may contain, besides, an aliphatic polymer and various additives. The aromatic polymer can be not only a single polymer but also a mixture of two or more polymers. Specific examples of the aromatic polymer are shown below:
(i) aromatic polyesters such as polyethylene terephthalate, polybutylene terephthalate and poly(ethylene-2,6-naphthalate); and poly(arylate)s composed of an aromatic dicarboxylic acid, bisphenol (A or S) and, optionally, a hydroxy aromatic carboxylic acid;
(ii) aromatic polyamides such as polymetaphenylene isophthalamide and paraphenylene isophthalamide;
(iii) aromatic polyimides composed of at least one aromatic tetracarboxylic acid dianhydride such as pyromellitic acid dianhydride, diphenyltetracarboxylic acid dianhydride or the like and at least one diamine such as hexamethylenediamine, xylylenediamine, phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylmethane or the like;
(iv) polyphenylene ether, polyphenylene sulfide, polyphenylene ether ether ketone, polyetherimide, polyphenylene sulfide; aromatic epoxy resins;
(v) bisphenol type polycarbonates;
(vi) polystyrenes;
The above aromatic polymers may be respective copolymers or mixtures with other polymers. For example, they may be a mixture of the above polycarbonate with a polystyrene.
Besides the above illustrated aromatic polymers, there are also included, in the scope of the aromatic polymer of the present invention, those polymers obtained by polymerizing styrene, methylstyrene, benzyl methacrylate, phenyl methacrylate or o-methylphenylmaleimide with methyl methacrylate and containing an aromatic ring-containing monomer in an amount of 20% by weight or more.
Preferably, the aromatic polymer is substantially linear. It can be in any of a crystal form, a semicrystal form and an amorphous form.
In the present invention, the molded article composed of a polymer composition containing an aromatic polymer can have any shape. However, the portion of the molded article to be irradiated with an ultraviolet laser beam is preferably planar. In general, the shape of the molded article is suitably a film, a sheet, a plate or a board each advantageously having a thickness of particularly about 1 .mu. to about 2 mm, preferably about 5 .mu. to about 1.5 mm. These film and sheet may be used as they are but also used as a laminated film with other film or sheet.
The film, sheet, plate or board may have been drawn or undrawn. When a drawn product is preferred, it may be a uniaxially drawn or biaxially drawn product.
In the present invention, the ultraviolet laser beam applied to the surface of the molded article has a wavelength of about 150 nm to about 380 nm, preferably about 180 nm to about 320 nm. The light source thereof can be not only a laser beam of single wavelength but also a beam of a plurality of wavelengths. As the density of the ultraviolet laser beam, there is used a power density of at least 10.sup.4 w/cm.sup.2, preferably at least 10.sup.5 w/cm.sup.2.
As the ultraviolet laser beam, there can be specifically used, for example, laser beams of F.sub.2 laser, ArF laser, KrCl laser, KrF laser, XeCl laser, N.sub.2 laser, XeF laser, dye laser, etc; laser beams emitted from high-frequency transformers such as copper vapor laser, YAG laser and the like; a laser beam emitted from a waveguide type excimer laser used as a light source for write-once type optical information recording, and a beam emitted from a high power discharge tube containing argon or xenon, capable of radiating a large capacity beam (e.g. 10-40 KJ/pulse) in a large area in a short time.
Meanwhile in the present invention, when the aromatic polymer is a linear polymer constituted by a recurring unit containing at least one polycyclic condensed aromatic ring or diphenyl ring, it is sufficient that the ultraviolet laser beam has a wavelength of about 150 nm to about 380 nm; the beam need not have a high power density and there can be used, for example, a high pressure mercury lamp, a carbon arc lamp, a mercury resonance lamp, etc. all of low power density.
In the present invention, the ultraviolet laser beam is applied onto the surface of the molded article at a power density of at least 10.sup.4 w/cm.sup.2. At that time, the fluence of the beam is lower than the threshold.
The threshold is a value indicating a minimum fluence (J/cm.sup.2.pulse) at which a molded article causes etching when the surface of the molded article has been irradiated with an ultraviolet laser beam, and it takes a given value when the wavelength of the beam and the type of the polymer in the molded article are selected.
In other embodiment of the present invention, when there is intended a molded article with an at least partially dicolored surface, an ultraviolet laser beam having a wavelength of about 150 nm to about 380 nm can be applied to a molded article at a density of at least of 10.sup.4 w/cm.sup.2 at a fluence which is 300% or less of the threshold, to the extent that the irradiated portions of the molded article whiten or blacken.
In the irradiation of the molded article with an ultraviolet laser beam according to the present invention, when precise processing is required, it is possible to employ a technique, process or equipment of lithography such as photomask, aligner used for wafer exposure or the like. For example, a transparent plate or sheet (these are hereinafter referred to as "light-transmitting plate") is placed in tight contact with the surface of a molded article or at a very small distance (about 1 mm or less) from the surface; an ultraviolet laser beam is transmitted through the transparent plate or sheet; and by the transmitted beam, the surface of the molded article can be modified precisely.
The light-transmitting plate can be any plate as long as it is of a transparent material having a thickness of several .mu.m to several mm and can transmit the large portion of a light applied. As the material of the light-transmitting plate, there can be used, for example, quartz, calcium fluoride, magnesium fluoride, lithium fluoride, a polyolefin, a polymethyl methacrylate or a poly(4-methylpentene-1). When an ultraviolet laser beam of long wavelength is applied, there can further be used, as the light-transmitting plate, a material which has substantially no absorbability for a light of long wavelength, such as glass, cellulose acetate or polystyrene.
When the light-transmitting plate is used in application of the ultraviolet laser beam, the surface modification, especially discoloration of the molded article is accelerated strikingly as compared with when no light-transmitting plate is used. It is difficult to theoretically explain this action of the light-transmitting plate, but the object of the present invention can be achieved very efficiently by the use of the light-transmitting plate-photomask.
As the light exposure method for irradiating the molded article with an ultraviolet laser beam, there are generally known a method in which light exposure is effected with a photomask placed in vacuum contact or soft contact with a work, and an exposure method by non-contact projection (proximity mode). In any of these methods, the surface modification and discoloration of the molded article can be accelerated by using a photomask as a light-transmitting plate.
In irradiating the surface of a molded article with an ultraviolet laser beam according to the present invention, the atmosphere can be any of "in air", "in an inert gas", "under vacuum" or "under pressure". In some cases, it is preferable to effect irradiation by ultraviolet laser beam at an elevated temperature to enhance the irradiation efficiency. As other means to enhance the efficiency of irradiation by ultraviolet laser beam, a method of adding a photosensitizer to a polymer composition beforehand is effective. As such a photosensitizer, there can be mentioned, for example, benzoin pyrene, benzophenone, benzotriazole, dyes, etc.
The fluence as one condition of irradiation by ultraviolet laser beam is an important factor. An appropriate fluence (energy density) differs depending upon the purpose of the surface modification of the molded article.
For example, the irradiation conditions used when the surface of a film is modified from hydrophobicity to hydrophilicity are generally milder than the conditions used when the surface is discolored, as shown in Tables 1-3 of Example 1 which is described later. Meanwhile, when the purpose of the surface modification of a molded article is to modify the electrical or chemical properties of the surface, the power density and fluence of an ultraviolet laser beam used for irradiation of the molded article are important factors. The power density used in irradiation is appropriately 10.sup.4 w/cm.sup.2 -30 MW/cm.sup.2, particularly 10.sup.5 w/cm.sup.2 -20 MW/cm.sup.2. The fluence used in irradiation is 10% or more, preferably 20% or more of the threshold, and the upper limit is 300%, preferably 200%.
When the modification is effected to achieve discoloration, the irradiation conditions differ by the objective of the discoloration, i.e. blackening or whitening-and-devitrification. In the case of the former, high level blackening can often be obtained by controlling the power density and the fluence per pulse low within the above ranges and increasing the pulse frequency.
Meanwhile when the modification is effected to achieve whitening-and-devitrification in order to obtain a molded article having drawability, a good result can be obtained either by employing a fluence per pulse which is lower than employed when the modification is effected to achieve blackening, or by employing a fluence per pulse which is higher than employed when the modification is effected to achieve blackening.
As mentioned previously, the molded article of the present invention can take various shapes, for example, a film, a sheet, a disc, a fiber, etc. However, when the molded article is used as a recording layer of an information recording medium, a glass plate or a metal (e.g. aluminum) plate may be used as a substrate of the recording medium. In this case, a polymer composition is dissolved in an appropriate solvent, the resulting solution is coated on a substrate such as glass or the like, then the solvent is removed (evaporated), whereby a recording medium material comprising a substrate and a recording layer formed thereon can be prepared. In such a recording medium material, a metal an oxide, an organic compound or the like can be arranged on the recording layer or between the recording layer and the substrate, for amplification of reflection or protection of recording layer. However, in the most simple structure, there is used, as a substrate, a composition which is the same as the polymer composition constituting the molded article.
As mentioned previously, when the molded article is subjected to surface modification by ultraviolet laser beam according to the present invention, it is not necessary to draw the molded article simultaneously with or after the irradiation with the ultraviolet laser beam, and the surface modification can be effected only by the irradiation. In some cases, the effect of the irradiation is rather enhanced by subjecting the molded article to a preliminary treatment before the irradiation by ultraviolet laser beam. The drawing and orientation treatment of the molded article is a preferable example of the preliminary treatment. This drawing can be uniaxial or biaxial, and the biaxial drawing can be sequential biaxial or simultaneous biaxial. In the case of uniaxial drawing, the preferable draw ratio differs by the type of polymer composition, etc. but is about 2-5 times in the case of polyethylene terephthalate. In the case of biaxial drawing and orientation, the preferable areal draw ratio of polyethylene terephthalate is 5-20 times. The drawing temperature is 80.degree.-160.degree. C. in the case of polyethylene terephthalate and, after the drawing, there is ordinarily effected a heat treatment at 120.degree. -240.degree. C. The heat-treated molded article may then be used for irradiation, or, the heat treatment may be effected after irradiation. In some cases, the heat treatment may be omitted. As the preliminary treatment other than drawing, there is the formation of latent crystal nuclei in the molded article to be surface-modified, by heating the article to at least around its crystallization temperature.
It is also an effective example of the preliminary treatment to form crystal nuclei in the molded article by immersing the molded article in an appropriate solvent. For example, when the molded article is an amorphous polyethylene-2,6-naphthalate film, dioxane is used as the solvent and the molded article is immersed therein, for example, at about 50.degree. C. for about 10 minutes, whereby crystal nuclei can be formed in the molded article.
According to the process of the present invention, the surface of a molded article can be modified electrically or discolored as mentioned above, and further can be modified in chemical and physical properties such as adhesion, friction coefficient and the like.
To enable the use of a high fluence, it is desirable to effect irradiation by using a convex lens and appropriately selecting the distance between light source and lens and the distance between lens and surface to be irradiated so that a desired fluence can be obtained at said surface. Meanwhile, to enable the use of a low fluence, it is sufficient to use a concave lens and appropriately select the above two distances.